1. Field of the Invention
The invention relates to a technique for performing a driving control of an engine valve of an internal combustion engine using electromagnetic force.
2. Description of the Related Art
As a method for driving an intake valve and an exhaust valve which are engine valves of an internal combustion engine, an electromagnetically driving method in which the engine valves are driven using electromagnetic force is known. According to the electromagnetically driving method, opening/closing timing of the intake valve and the exhaust valve can be easily optimized in accordance with an operating state of the internal combustion engine (hereinafter, referred to simply as “engine operating state”), and combustion efficiency of the internal combustion engine can be improved. However, the electromagnetically driving method has not been widely used, and various techniques are proposed for putting the electromagnetically driving method to practical use.
For example, in order to reduce an operation noise which occurs when an electromagnetically driven valve is operated to be opened/closed, a technology is proposed, in which a value of current to be supplied to an electromagnet is calculated such that an actual speed of a movable portion becomes equal to a target speed, and energization of the electromagnet is controlled according to the calculated value of current (refer to Japanese Patent Laid-Open Publication No. 2000-234534, and Japanese Patent Laid-Open Publication No. 2001-221022). Also, another technology is proposed, in which valves are divided into valve groups such that each valve group includes valves whose opening periods do not overlap with each other, and a switching device is provided for each valve group so as to function as a driver for all the valves in each valve group (refer to Japanese Patent Laid-Open Publication No. 9-189209).
In order to reduce the operation noise, it is generally effective to shorten a control cycle of a processing unit such as a central processing unit (hereinafter, referred to simply as “a CPU”) included in a controller (hereinafter, referred to simply as “an ECU”) so that control for the electromagnetically driven valve is performed at a high speed, and the movable portion is smoothly seated when the electromagnetically driven valve is operated to be opened/closed. However, for example, an on-vehicle CPU which is easily available, and whose operating frequency is approximately several tens of megahertz to several hundred megahertz does not have an ability to perform different controls for plural electromagnetically driven valves in a satisfactorily meticulous manner. Therefore, it is conceivable to increase the number of CPUs. However, in the case of a design in which the number of CPUs is simply increased without considering optimization of the opening/closing timing, there is a problem in terms of cost.